Determining COVID-19 vaccine effectiveness among health care workers in Wales

In response to the ongoing coronavirus disease 2019 (COVID-19) pandemic, scientists have worked at an unprecedented speed to develop effective vaccines to contain the pandemic.

This pandemic has been caused by the rapid spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Although clinical trials have predicted high vaccine efficacy, the percentage varies in real-world conditions.

Background

To evaluate the efficacy of the COVID-19 vaccines in real-world settings, certain factors must be considered, for example, the number of individuals willing to be vaccinated (uptake), reduction in serious outcomes after vaccination (effectiveness), and how long the immune protection is sustained (waning).

Health care workers (HCWs) are at a higher risk of exposure to SARS-CoV-2 compared to the general population. Therefore, studying this group could provide a better understanding of the effectiveness of a newly developed COVID-19 vaccine, in an environment where the risk of exposure is greater. HCWs, in Wales, are required to take a polymerase chain reaction (PCR) test if they show symptoms or were in close contact with a COVID-19 patient.

In Wales, the COVID-19 vaccination program started on the 8th of December, 2020. Individuals were vaccinated with any one of the vaccines, i.e., BNT162b2 mRNA (Pfizer-BioNTech), ChAdOx1 adenoviral (Oxford-AstraZeneca), or mRNA-1273 (Moderna), as per the availability. Every eligible individual was given two doses of vaccines, with an interval of 8–12 weeks between doses. Subsequently, from the 20th of September 2021, COVID-19 booster vaccinations started and HCWs were prioritized for vaccination. A booster vaccination was administered to HCWs, six months after their second dose.

A new study

Scientists constructed a national cohort of HCWs in Wales (UK), from 7th December 2020 to 30th September 2021. This cohort was analyzed for a better understanding of COVID-19 vaccine uptake, effectiveness, and waning of the BNT162b2 vaccine. This study was followed up to twenty-six weeks post-vaccination and has been published in the journal Vaccine. The authors collected national-scale data that included 82,959 health care workers in Wales.

The study cohort revealed an overall high vaccine uptake and significant vaccine effectiveness of BNT162b2, among HCWs. Researchers observed that HCWs who received two doses of the BNT162b2 vaccine were significantly protected from COVID-19 infection, even though they were highly exposed to SARS-CoV-2 patients. This vaccine was reported to be 85% effective against COVID-19 infection. Scientists found evidence of waning of vaccine effectiveness. They found that the effectiveness reduced to 53% by six months after the second dose.

The main strength of this study is its large sample size. The majority of the studies available so far have used smaller sample sizes, as well as measured the vaccine effectiveness by the self-reported data. The current study is unique because it provides national population estimates over time of vaccine uptake as well as vaccine effectiveness for HCWs with respect to PCR-test confirmed infection. Another important aspect of this study is that it measures vaccine uptake and effectiveness across a range of sociodemographic characteristics in a large study cohort of HCWs.

Scientists reported a differential rate of vaccine uptake across staff groups and age. This implies the presence of various factors, such as people’s vulnerability profile, age, and social factors, that influences vaccine uptake of HCWs. The findings of this study are in line with a previous study that revealed older HCWs were more inclined to be vaccinated compared to a younger group. Additionally, this study observed that estates and ancillary staff were less likely to be vaccinated than nursing and midwifery staff. Researchers found that vaccine uptake was lower for deprived groups.

The authors reported that the BNT162b2 vaccine significantly reduced the risk of contracting infection, three weeks after the first dose of vaccine.

The study cohort clearly demonstrated the benefits of two doses of BNT162b2 as it provided high immune protection. Scientists also indicated the possibility of reduction of COVID-19 infection due to non-pharmaceutical interventions, which were effective during the study period.

Scientists were unable to determine the vaccine effectiveness against SARS-CoV-2 variants, owing to the lack of relevant data. However, during the study period, the Alpha variant was the dominant circulating strain in Wales, and was gradually replaced by the Delta variant. The authors surmised that the BNT162b2 vaccine protected HCWs against SARS-CoV-2 variants, but the level of protection varied from one variant to another.

Conclusion

One of the advantages of the national cohort of HCWs was that it helped scientists to provide a holistic picture of vaccine uptake and effectiveness. The longitudinal design of this study allowed scientists to analyze data from the same individuals over time. This reduced the problems of variations that could be generated if different subjects were studied under the same conditions.

The authors revealed that two doses of vaccine protected HCWs despite being at a higher risk of exposure to COVID-19.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.